1. Technical Field
This invention is generally directed to the fields of cardiac surgery and interventional cardiology, and particularly, to implants, catheters and methods suited for improving blood flow to a heart muscle and the formation of new blood vessels by Trans Myocardial Revascularization (TMR).
2. Description of Related Art
Symptomatic occlusive coronary artery disease that does not respond to medical or interventional treatment is a major challenge for cardiac surgeons and cardiologists. The discovery of sinusoidal communications within the myocardium (Wearns, 1993) has motivated researchers to attempt various methods for myocardial revascularization based on the existence of this vascular mesh network. These methods aimed at the delivery of oxygenated blood to the vicinity of the sponge-like sinusoidal plexus in order to restore blood flow to the ischemic myocardium. Several investigators have attempted to deliver oxygenated blood directly from the left ventricle into the myocardial sinusoids by employing needle acupuncture to create transmural channels. Trans Myocardial Revascularization (TMR) has been employed clinically (Mirhoseini, 1991) by utilizing a CO2 laser for creating transmural channels in the left ventricular myocardium. These channels are typically 1 mm in diameter and extend throughout the wall thickness (15 to 20 mm) of the ventricle. It has been hypothesized that TMR works by providing a fluid conduit for oxygenated blood to flow from the endocardiac surface (heart chamber) to the mycardium inner layers thus providing oxygenated blood to myocardial cells without requiring coronary circulation; as in reptiles. Animal studies in the canine model have demonstrated the feasibility of this approach. In these studies, an increase in survival rate was demonstrated in dogs that had transmural channels and ligated coronary arteries.
While clinical studies have demonstrated improvements in patient status following TMR, histological studies indicate that the channels created for TMR tend to close shortly after the procedure. Randomized, prospective clinical trials are underway to examine the merit of TMR compared to medical treatment. In the meantime, research studies are being initiated to provide an understanding of the mechanism by which TMR actually works.
It would be desirable to develop means for maintaining the patency of TMR channels or producing new blood vessels within the myocardium. Furthermore, it would be desirable to create channels for TMR without requiring the use of an expensive and bulky laser system, such as currently available CO2 laster systems. This invention provides the desired means for producing trans myocardial channels that are likely to remain patent, and that do not require laser application for generating these channels.
Specifically, the objective of the present invention is to generate needle-made channels or space in the ischemic heart wall, and to deliver or place in these channels (or space) an array of TMR implants in order to provide improved means for supplying blood nutrients to ischemic myocardial tissue. Nutrients flow to the channels having implants therein from the ventricular cavity help to form new blood vessels, and may diffuse from the side ports of the TMR implant to the myocardial tissue through the needle-made channels. The disclosed TMR approach of producing needle-made, implanted channels is supported by the recent scientific evidence (Whittaker et al, 1996) that needle-made transmural channels can protect ischemic tissue. Whittaker et al. assessed myocardial response at two months to laser and needle-made channels in the rat model, which has little native collateral circulation. They found that channels created by a needle can protect the heart against coronary artery occlusion, and that these channels provide greater protection to ischemic tissue than channels created by laser. The limitation of needle-made channels is early closure (Pifarre, 1969). The implanting approach of the present invention offers a possible solution to the early closure problem, while taking advantage of simple and effective means for inserting such TMR implants.